In optical fiber transmission, wavelength dispersion is one main factor that causes signal degradation. Compensation for wavelength dispersion needs to be performed optically, but in the case of using a method in which a dispersion compensation fiber that depends on the distance of the optical fiber is physically inserted, an increase in operational cost is incurred. Also, in the case of using a method of performing compensation through digital signal processing, an apparatus for performing digital signal processing is expensive, and therefore it has been difficult to use this method with an access line that is required to have a lower cost. Furthermore, in a network topology using a Point-to-MultiPoint (PtMP) scheme such as a PON (Passive Optical Network), in the case of performing compensation for wavelength dispersion of paths from an OLT (optical line terminal) to respective ONUs (optical network units), multiple dispersion compensation fibers corresponding to respective distances are needed.
PTL1 discloses a technique in which multiple wavelength dispersion compensators are included in an OLT and are switched between according to the distances of the ONUs.